Problem: $ E = \left[\begin{array}{rrr}2 & 2 & 0 \\ 2 & 0 & 0 \\ 0 & 2 & 2\end{array}\right]$ What is $ E^{-1}$ ?
Explanation: $ = \left[\begin{array}{rrr}0 & \frac{1}{2} & 0 \\ \frac{1}{2} & -\frac{1}{2} & 0 \\ -\frac{1}{2} & \frac{1}{2} & \frac{1}{2}\end{array}\right]$